The operation of the high resolution scanning transmission electron microscope (STEM) at Johns Hopkins as a Biotechnology Resource Facility is proposed. The STEM will be available to qualified users according to the priority decided by the Advisory Committee. The unique contrast mechanisms of the STEM will be applied to discovering biological structure in isolated molecules, assemblies, and periodic aggregates. Recently developed techniques at image processing will be incorporated wherever useful. Specific heavy metal-organic reactions already developed in this lab and in the core research will be used to provide structure labels in many of the projects. The characterization of heavy element-organic reactions to be used as structure labels, the measurement of movement of heavy element labels during microscopy, the use of energy loss spectroscopy to identify heavy element labels, and the effect of temperature down to 10 degrees K on the preservation of specimen and labels, will form the core research at the facility. Biological structure studies already proposed include contractile proteins, collagen, RNA polymerase, cell surface sugars, ribosomes, chromatin and fibrinogen.